Custom Wordpress Query Page - Custom Permalinks

class-CustomEndpoint.php

<?php
/**
 * Custom Wordpress Query Page - Custom Permalinks
 * @author Aaron Olin
 */
if (! class_exists('CustomEndpoint')) {
    class CustomEndpoint {
        protected static $_instance = null;
        protected $templateFile;        
        
        protected $endpointRoot;
        protected $apiRewritePermalink;        
        protected $apiRewriteRule;
        protected $rewriteRules = [];        


        public function __construct($templateFile, $endpointRoot, $rewriteRules = [])
        {
            $this->templateFile = $templateFile;
            $this->endpointRoot = $endpointRoot;
            $this->rewriteRules = $rewriteRules;

            $this->setApiRewritePermalink();
            $this->setApiRewriteRule();

            // b/o: API Endpoint
            add_action('init', [$this, 'addApiEndPoint']);
            add_filter('query_vars', [$this, 'validQueryVars']);
            add_filter('template_include', [$this, 'handleApiRequest']);
            // e/o: API Endpoint
        }

        public function setApiRewritePermalink()
        {
            $this->apiRewritePermalink = $this->endpointRoot . '/';
            
            $ruleCount = count($this->rewriteRules);
            
            for($i=0; $i<= $ruleCount; $i++) {
                $this->apiRewritePermalink .= '([^\\/]*)/?';    
            }
        }

        public function apiParameterRulesBuilt()
        {
            $rules = '';
            $i = 1;
            foreach ($this->rewriteRules as $rule) {
                if ($i == 1) {
                    $rules .= "$rule=\$matches[$i]";
                } else {
                    $rules .= "&$rule=\$matches[$i]";
                }
                $i++;
            }

            return $rules;
        }

        public function setApiRewriteRule()
        {
            $this->apiRewriteRule = 'index.php?';
            $this->apiRewriteRule .= $this->apiParameterRulesBuilt();            
        }

        /**
         * Set the endpoint URL for concatenated CSS link
         */
        public function addApiEndPoint()
        {   
            $this->maybeFlushRewriteRules($this->apiRewritePermalink, $this->apiRewriteRule);

            $regex = $this->apiRewritePermalink;
            $location = $this->apiRewriteRule;
            
            $priority = 'top'; // use 'top' here or WP will send you to the page if 'bottom' is used;

            add_rewrite_rule($regex, $location, $priority);
        }

        /**
        * Specify safe variables to use with the endpoint. If a variable is not specified, it will not be available to $this->add_api_endpoint()
        *
        * @param  array $vars an array of query vars
        * @return array       an array of query vars
        */
        public function validQueryVars($vars)
        {
            foreach ($this->rewriteRules as $_var) {
                $vars[] = $_var;
            }
            
            return $vars;
        }

       /**
        * Handle the API requests and route where necessary
        *
        * @return string wp template URL which should always be returned for non-api calls
        */
        public function handleApiRequest($template)
        {            
            $firstVar = get_query_var('firstvar', null);
            // $secondVar = get_query_var('secondvar', null);
            // $thirdVar = get_query_var('thirdvar', null);

            if ($firstVar) {              
                $template = get_stylesheet_directory() . '/' . $this->templateFile;
            }

            return $template; // must be returned, always!
        }

        /**
         * Check if specific rewrite rule exists, if not, then we'll flush the permalinks to add it
         *
         * @param  string $rewriteKey   the rewrite array key value to check for
         * @param  boolean $force       skip checking for rewrite key and force the flush
         * @return null
         */
        public function maybeFlushRewriteRules($rewriteKey, $rewriteRule, $force = false)
        {   
            if ($force) {
                flush_rewrite_rules(true);
                return;
            }

            $registeredRewriteRules = get_option('rewrite_rules');

            if (! array_key_exists($rewriteKey, $registeredRewriteRules) || ! $this->in_array_r($rewriteRule, $registeredRewriteRules)) {
                flush_rewrite_rules(true);
            }
        }

        /**
         * a multidimensional version of PHP's in_array()
         * https://gist.github.com/Billy-/bc6865066981e80e097f
         * 
         * @param  string   $needle   [description]
         * @param  array    $haystack [description]
         * @param  boolean  $strict   [description]
         * @return boolean            [description]
         * usage:   $multi_array = [ ["foo", "bar"], ["baz", "qux"] ];
         *          echo in_array_r("baz", $multi_array) ? 'found' : 'not found';
         */
        public function in_array_r($needle, $haystack, $strict = false) {
            foreach ($haystack as $item) {
                if (($strict ? $item === $needle : $item == $needle) || (is_array($item) && $this->in_array_r($needle, $item, $strict))) {
                    return true;
                }
            }

            return false;
        }


        public static function instance($templateFile, $endpoint, $rewriteRules = [])
        {
            if (is_null(self::$_instance)) {                
                self::$_instance = new self($templateFile, $endpoint, $rewriteRules);
            }

            return self::$_instance;
        }

    }

    function endpointRedirect($templateFile, $endpoint, $rewriteRules) {
        return CustomEndpoint::instance($templateFile, $endpoint, $rewriteRules);
    }
} // e/o: if class_exists


/** 
 * register the custom endpoint with these properties
 * Example: You can access the following page: http://domain.dev/myendpoint/firstvar_value/secondvar_value/thirdvar_value
 * Tip 1: Use the handleApiRequest method to handle the custom query vars (firstvar,secondvar, thirdvar)
*/
if (function_exists('endpointRedirect')) {
    endpointRedirect(        
        'redirect-myendpoint.php', // uses the template file redirect-myendpoint.php located in root of Wordpress theme
        'myendpoint', // the custom endpoint permalink slug
        ['firstvar', 'secondvar', 'thirdvar'] // rewrite rules
    );    
}